The present invention generally relates to lighted displays for displaying images, and more particularly to the backlighting of image generating displays, such as active matrix liquid crystal displays which are useful for head up displays.
Electronic image displays are commonly illuminated by backlighting the display for direct viewing from the front or for viewing in a head up display (HUD) system. HUD systems have been widely known and used in military and commercial aircraft applications. More recently, HUD systems have been employed in automotive vehicles to project an image for display in front of the vehicle driver so that the image is viewable through the front windshield. The HUD system thus serves as an alternative to displaying the image on a display unit generally located in the instrument panel of the vehicle.
In automotive applications, passive displays, such as active matrix liquid crystal displays (AMLCD), are illuminated by applying backlight illumination to the backside of the electronic display. Since HUDs typically project a light pattern generated by an image source and reflect the light pattern from a windshield generally having a low reflectivity, it becomes necessary to provide a high intensity light source, especially during daylight driving conditions which demand a very bright image source. Typically, the image source for a HUD includes a halogen bulb and an elliptical reflector such as is disclosed in U.S. Pat. No. 5,709,463. The aforementioned patent is hereby incorporated by reference.
In many conventional HUD systems, multiple images are generated by a single electronic display and only a portion of the display grid is actually used to project the images. The remaining portion of the display grid, which is not used to display any image, is generally colored black. With conventional backlighting approaches, the light pattern is generally configured to illuminate the entire backside of the electronic display grid. Accordingly, not only is the lighted portion of the display grid illuminated, but the black non-lighted portion of the grid is also illuminated in many conventional displays. The non-lighted black colored portion of the display grid absorbs light energy illuminated thereon, and the absorbed light energy is converted to heat energy. Not only is this light not used for generating an image, but the heat build-up in the electronic display raises the operating temperature to excessive levels which may lead to damage or inoperability of the display.
It is therefore desirable to provide backlighting for a display, such as a liquid crystal display, which avoids problems associated with overheating of the display. It is further desirable to provide for backlighting for such a display which more efficiently utilizes the light energy. It is particularly desirable to provide for such backlighting for a display for use in HUD systems, such as those used in automotive vehicles.
The present invention provides for an image illumination apparatus for backlighting a portion of an electronic display. The apparatus comprises a light source for generating illuminating light, a light shielding medium located between the light source and a display, and an aperture formed in the light shielding medium for allowing the transmission of light generated by the light source to pass to a lit portion of the display. The light shielding medium prevents some of the light from being transmitted to non-lit portions of the display.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.